Degree of conversion of nano-hybrid resin-based composites with novel and conventional matrix formulation.

Objectives: This study aimed to determine the degree of conversion (DC) of two nano-hybrid resin-based composites (RBCs) with novel monomer composition based on dimer acid derivates (hydrogenated dimer acid) and tricyclodecane-urethane structure compared to three nano-hybrid materials containing conventional matrices. DC was evaluated at 0.1, 2, and 6 mm depth at varying irradiation times (10, 20, and 40 s) and layering techniques (bulk and incremental). Materials and methods: DC was measured in real time by a Fourier transform infrared spectroscopy (FTIR) spectrometer with attenuated total reflectance accessory. The FTIR spectra were recorded on the bottom of the samples in real time for 5 min from photoinitiation. Results were compared using one- and multiple-way ANOVA, Tukey's HSD post hoc test ( α = 0.05), and partial eta-squared statistic. Results: After 5 min of measurement, DC showed no significant difference by varying cure time for specimens of 0.1 mm thickness. At 2 mm depth, the DC significantly increased after a cure time of 20 s compared to 10 s, remaining equal after 40 s of irradiation. At 6 mm depth, bulk curing showed significantly lower DC compared to incremental curing for all polymerization times. Specimen geometry revealed a strong effect on DC ( η = 0.90) followed by curing time ( η = 0.39). Conclusions: The RBCs containing the dimer acid and tricyclodecane-urethane structure showed a relatively low decrease of DC with increasing incremental thickness compared to the conventionally formulated materials. The former reached the highest DC among the tested materials. Clinical relevance: For the tested RBCs, increments of 2 mm and irradiation time of at least 20 s may be recommended for clinical practice. The two materials containing novel monomer composition might be applied for enlarged increments because of the low decrease of DC they demonstrated for 6-mm increments. [ABSTRACT FROM AUTHOR]